Surgical instrument with safety mechanism

ABSTRACT

A surgical instrument including a handle assembly, a safety mechanism, an elongated body portion and a head portion is disclosed. The handle assembly includes a stationary handle, an approximation mechanism, and a firing trigger. A lever of the safety mechanism is movable between a first position where the firing trigger is prevented from being actuated, and a second position where the firing trigger is able to be actuated. A first jaw member of the head portion is movable in relation to a second jaw member of the head portion between spaced and approximated positions. Movement of the first jaw member in relation to the second jaw member from the approximated position towards the spaced position causes the lever of the safety mechanism to move from its second position to its first position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 14/180,654 filed Feb. 14, 2014, now U.S. Pat. No. 8,833,630, which is a continuation of U.S. patent application Ser. No. 13/407,972 filed Feb. 29, 2012, now U.S. Pat. No. 8,684,248, which is a continuation of U.S. patent application Ser. No. 12/781,622 filed May 17, 2010, now U.S. Pat. No. 8,146,790, which claims benefit of U.S. Provisional Application No. 61/224,855 filed Jul. 11, 2009, and the disclosures of each of the above-identified applications are hereby incorporated by reference in their entirety.

This application claims priority to provisional application Ser. No. 61/224,855, filed Jul. 11, 2009, the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates generally to a surgical instrument for applying surgical staples to body tissue. More particularly, the present disclosure relates to a surgical stapling instrument suitable for performing circular anastomosis and/or treatment to internal walls of hollow tissue organs.

2. Background of Related Art

Anastomosis is the surgical joining of separate hollow organ sections. Typically, an anastomosis procedure follows surgery in which a diseased or defective section of hollow tissue is removed and the remaining end sections are to be joined. Depending on the desired anastomosis procedure, the end sections may be joined by either circular, end-to-end, end-to-side, or side-to-side organ reconstruction methods.

In a circular anastomosis procedure, the two ends of the organ sections are joined by means of a stapling instrument which drives a circular array of staples through the end section of each organ section and simultaneously cores any tissue interior of the driven circular array of staples to free the tubular passage. Examples of instruments for performing circular anastomosis of hollow organs are described in U.S. Pat. Nos. 7,303,106, 6,053,390, 5,588,579, 5,119,983, 5,005,749, 4,646,745, 4,576,167, and 4,473,077, each of which is incorporated herein in its entirety by reference. Typically, these instruments include an elongated shaft having a handle portion at a proximal end to actuate the instrument and a staple holding component disposed at a distal end. An anvil assembly including an anvil rod with attached anvil head is mounted to the distal end of the instrument adjacent the staple holding component. Opposed end portions of tissue of the hollow organ(s) to be stapled are clamped between the anvil head and the staple holding component. Typically, a first actuation mechanism is used to approximate the anvil head and the staple holding component to clamp the tissue. The clamped tissue is stapled by driving one or more staples from the staple holding component so that the ends of the staples pass through the tissue and are deformed by the anvil head. Typically, a second actuation mechanism is used to fire the staples. It is also common for an annular knife to be concurrently advanced to core tissue within the hollow organ to free a tubular passage within the organ.

Besides anastomosis of hollow organs, surgical stapling instruments for performing circular anastomosis have been used to treat internal hemorrhoids in the rectum. Typically, during use of a circular stapling instrument for hemorrhoid treatment, the anvil head and the staple holding component of the surgical stapling instrument are inserted through the anus and into the rectum with the anvil head and the staple holding component in an open or unapproximated position. Thereafter, a pursestring suture is used to pull the internal hemorrhoidal tissue towards the anvil rod. Next, the anvil head and the staple holding component are approximated to clamp the hemorrhoid tissue between the anvil head and the staple holding component. The stapling instrument is fired to remove the hemorrhoidal tissue and staple the cut tissue. In other uses for hemorrhoid surgery, the stapling instrument is used to remove tissue just above the hemorrhoids in order to pull the hemorrhoids back up inside the rectum and reduce the symptoms. The staples interrupt the blood flow of the superior hemorrhoidal arterial branches, cutting off the blood supply to the tissue, thus causing the hemorrhoids to shrink.

Some surgical stapling instruments include a safety device that prevents staples from being fired before approximation of the anvil head and the staple holding component.

SUMMARY

The present disclosure relates to a surgical instrument comprising a handle assembly, a safety mechanism, an elongated body portion and a head portion. The handle assembly includes a stationary handle, an approximation mechanism, and a firing trigger. A lever of the safety mechanism is movable between a first position where the firing trigger is prevented from being actuated, and a second position where the firing trigger is able to be actuated. An approximation mechanism moves the first jaw member in relation to the second jaw member from a spaced position to an approximated position, wherein movement of the first jaw member in relation to the second jaw member from the approximated position towards the spaced position causes the lever to move from its second position to its first position.

In an embodiment, the lever is biased towards its first position. In a preferred embodiment, the safety mechanism includes a latch disposed on the lever and a latch retainer disposed on the stationary handle, wherein the latch and latch retainer are configured to releasably maintain the lever in its second position. The latch retainer can be biased proximally.

In preferred embodiments, a predetermined amount of movement of the first jaw member from the approximated position towards its spaced position causes distal movement of the latch retainer to release the latch.

In some embodiments, the safety mechanism includes a plate disposed in mechanical cooperation with the stationary handle, and the plate is biased distally. A lip of the plate preferably prevents movement of the lever towards its second position.

The lever is preferably configured to mechanically engage the firing trigger when the lever is in its first position, the firing trigger fires a plurality of fasteners from the first jaw into contact with the second jaw.

The present disclosure provides in another aspect a surgical instrument comprising a handle assembly including a stationary handle, an approximation mechanism, and a firing trigger for firing a plurality of fasteners. A safety mechanism is disposed in mechanical cooperation with the handle assembly and is movable between a first position to prevent firing of the fasteners and a second position to enable firing of the fasteners. The safety mechanism is retained in the second position. An elongated body portion extends distally from the handle assembly. A head portion is disposed adjacent a distal end of the elongated body portion and includes a first jaw member and a second jaw member, the first jaw member being movable in relation to the second jaw member between spaced and approximated positions. An approximation mechanism moves the first jaw member in relation to the second jaw member from a spaced position to an approximated position, wherein movement of the first jaw member in relation to the second jaw member from the approximated position towards the spaced position prior to firing of the fasteners causes the safety mechanism to be released to move from its second position to its first position.

In some embodiments, the plurality of fasteners are retained in the second jaw.

In preferred embodiments, the safety mechanism includes a lever retained by a latch retainer in the second position. Preferably, a predetermined amount of movement of the first jaw member from the approximated position towards the spaced position causes distal movement of the latch retainer to release the latch.

In some embodiments, the safety mechanism includes a plate disposed in mechanical cooperation with the stationary handle, the plate being biased distally and moved by the movement of the approximation mechanism. The lip of the plate in some embodiments prevents movement of the lever towards its second position.

DESCRIPTION OF THE DRAWINGS

Various embodiments of the presently disclosed surgical stapling instrument are disclosed herein with reference to the drawings, wherein:

FIG. 1 is a perspective view of the presently disclosed surgical stapling instrument illustrated in an unapproximated position, in accordance with an embodiment of the present disclosure;

FIG. 2 is a perspective view of the surgical stapling instrument of FIG. 1 illustrated in an approximated position;

FIG. 3 is a side view of the surgical stapling instrument of FIGS. 1 and 2 illustrated in a fired position;

FIG. 4 is an longitudinal, cross-sectional view of a portion of the surgical stapling instrument in the unapproximated position and a first portion of a safety mechanism in a first position;

FIG. 5 is an longitudinal, cross-sectional view of a portion of the surgical stapling instrument in the unapproximated position and a second portion of the safety mechanism in a first position;

FIG. 6 is an longitudinal, cross-sectional view of a portion of the surgical stapling instrument in the unapproximated position and the first portion and the second portion of the safety mechanism in the first position;

FIG. 7 is a longitudinal, cross-sectional view of a portion of the surgical stapling instrument in the approximated position and the first portion of the safety mechanism in a second position;

FIG. 8 is a longitudinal, cross-sectional view of a portion of the surgical stapling instrument in the approximated position and the second portion of the safety mechanism in a second position;

FIG. 9 is a longitudinal, cross-sectional view of a portion of the surgical stapling instrument in the approximated position and the first portion and the second portion of the safety mechanism in the second position;

FIG. 9A is an enlarged view of a portion of the surgical stapling instrument of FIG. 9; and

FIG. 10 is a perspective view of a safety plate and latch retainer of the second portion of the safety mechanism as illustrated in FIGS. 5, 6, 8, 9 and 9A.

DETAILED DESCRIPTION

Embodiments of the presently disclosed surgical stapling instrument will now be described in detail with reference to the drawings in which like reference numerals designate identical or corresponding elements in each of the several views.

Throughout this description, the term “proximal” will refer to the portion of the instrument closer to the operator and the term “distal” will refer to the portion of the instrument farther from the operator.

FIGS. 1-3 illustrate one embodiment of the presently disclosed surgical stapling instrument and is generally referred to as reference number 10. Briefly, surgical stapling instrument 10 includes a handle assembly 12, an elongated body portion 14 including a curved elongated outer tube 14 a, and a head portion 16. Alternately, in some surgical procedures, e.g., the treatment of hemorrhoids, it is desirable to have a substantially straight body portion. It is contemplated herein that the length, shape and/or the diameter of body portion 14 and head portion 16 may also be varied to suit a particular surgical procedure.

With continued reference to FIGS. 1-3, handle assembly 12 includes a stationary handle 18, a firing trigger 20, and a rotatable approximation mechanism 22. Head portion 16 includes a first jaw member (e.g., an anvil assembly 30) and a second jaw member (e.g., a shell assembly 31). Anvil assembly 30 is movable in relation to shell assembly 31 between spaced and approximated positions.

With continued reference to FIGS. 1-3, in operation, rotation of approximation mechanism 22 causes movement of anvil assembly 30 in relation to shell assembly 31 between spaced (FIG. 1) and approximated (FIGS. 2 and 3) positions, as approximation mechanism 22 is mechanically engaged with anvil retainer 38 (FIG. 1), which is fastened to anvil assembly 30. It is envisioned that rotation of approximation mechanism 22 in a first direction (e.g., clockwise) causes proximal movement of anvil assembly 30 (i.e., towards its approximated position), and rotation of approximation mechanism 22 in a second opposite direction (e.g., counter-clockwise) causes distal movement of anvil assembly 30 (i.e., towards its spaced position). Details of the approximation are disclosed for example in U.S. Pat. No. 7,303,106, the entire contents of which are incorporated herein by reference.

Actuation of firing trigger 20 (i.e., pivoting in the direction of arrow “A” in FIG. 1), causes staples to be ejected from shell assembly 31 towards anvil assembly 30. That is, firing trigger 20 is disposed in mechanical cooperation with a pusher (not explicitly shown in the illustrated embodiments), such that actuation of firing trigger 20 causes advancement of the pusher into contact with the staples, which ejects the staples into staple deforming pockets of anvil assembly 30. Details of the firing are disclosed for example in U.S. Pat. No. 7,303,106, the entire contents of which are incorporated herein by reference.

Referring now to FIGS. 4-9, approximation mechanism 22 is mechanically engaged with a screw stop 40 and screw stop 40 is in mechanical cooperation with anvil assembly 30 (not shown). Here, rotation of approximation mechanism 22 in a first direction causes screw stop 40 to move proximally, which in turn causes proximal movement of anvil assembly 30. As screw stop 40 moves proximally, a portion 42 thereof (see FIG. 9A) urges a portion (i.e., a plate 250) of safety mechanism 200 proximally against the bias of a plate spring 260, as discussed in more detail below. As a result, a lever 210 pivots in the direction of arrow “C” in FIG. 6 to permit firing of surgical stapling instrument 10. That is, when lever 210 is in its first, blocking position (FIGS. 4-6), actuation of firing trigger 20 is prevented.

More particularly, and with continued reference to FIGS. 4-9, safety mechanism 200 (which is broken down into a first portion 200 a (FIGS. 4 and 7) and a second portion 200 b (FIGS. 5 and 8), discussed in further detail below, is disposed in mechanical cooperation with handle assembly 12 and maintains firing trigger 20 in an open position (FIGS. 4-6) until anvil assembly 30 and shell assembly 31 have been approximated. Safety mechanism 200 is also configured to prevent the actuation of firing trigger 20 when anvil assembly 30 is moved relative to shell assembly 31 from their approximated position towards their spaced position. That is, if the anvil assembly 30 and shell assembly 31 are in their approximated position (e.g., clamping tissue) and are then moved towards their spaced position (e.g., unclamping tissue), safety mechanism 200 prevents actuation of firing trigger 20 until anvil assembly 30 and shell assembly 31 return to their approximated position. Thus, as can be appreciated, safety mechanism 200 helps prevent staples from being fired prematurely.

Various components of safety mechanism 200 are shown in FIGS. 4-9, with several components omitted in some figures for clarity. FIGS. 4-6 illustrate safety mechanism 200 in its first, locking position. FIGS. 7-9 illustrate safety mechanism 200 in its second, unlocked position. For ease of viewing clarity, as noted above, safety mechanism 200 has been broken down into a first portion 200 a (shown individually in FIGS. 4 and 7) and a second portion 200 b (shown individually in FIGS. 5 and 8). Both first portion 200 a and second portion 200 b of safety mechanism 200 are shown in FIGS. 6 and 9.

With initial reference to FIGS. 4 and 7, first portion 200 a of safety mechanism 200 includes lever 210 having a latch 212, and a safety spring 230. Lever 210 is pivotably disposed with respect to stationary handle 18. Latch 212, which is shown integrally formed with lever 210, includes a tooth 214 having an angled surface 216 thereon. A distance “d” is defined between tooth 214 and a surface 216 of lever 210 (see FIG. 4).

A distal portion 222 of safety spring 230 is configured to mechanically engage (e.g., pivotably engage) an aperture 218 of lever 210. A proximal portion 224 of safety spring 230 engages (e.g., is pinned to) a portion of stationary handle 18. Safety spring 230 is configured to bias lever 210 in the substantial direction of arrow “B” in FIG. 4.

Second portion 200 b of safety mechanism 200 is illustrated in FIGS. 5 and 8. Second portion 200 b includes plate 250 (an enlarged view of which is shown in FIG. 10), plate spring 260, a latch retainer 270, and a retainer spring 280. Plate 250 is disposed within stationary handle 18 and, as discussed above, plate 250 is configured for engagement by a portion of screw stop 40. More specifically, as screw stop 40 moves proximally, screw stop 40 contacts a distal portion 252 of plate 250 (see FIGS. 9A and 10), thus creating a proximal force against plate 250. Plate spring 260, which is also disposed within stationary handle 18, is in mechanical cooperation with a proximal portion 254 of plate 250 and is configured to distally bias plate 250 against the proximal force exerted thereon by screw stop 40. A rib 44 is disposed within stationary handle 18 and is configured and positioned to limit the distal translation of plate 250 (see FIGS. 5, 8 and 9A). More specifically, at least one of tabs 253 (see FIG. 10) of plate 250 is configured to engage rib 44.

With continued reference to second portion 200 b of safety mechanism 200 in FIGS. 5 and 8, latch retainer 270 and retainer spring 280 are illustrated. Latch retainer 270 is disposed in mechanical cooperation with plate 250 and is slidably engaged therewith. Latch retainer has several detents to engage the wall adjacent opening 258 in plate 250. Retainer spring 280 is disposed with stationary handle 18 and is configured to bias latch retainer 270 proximally with respect to plate 250. It is envisioned that a distal portion 282 of retainer spring 280 mechanically engages a portion 256 of plate 250 (see FIG. 10). As discussed in detail below, the interaction between latch retainer 270, retainer spring 280 and plate 250 is configured to allow releasable engagement between latch 212 and latch retainer 270. A proximal portion 284 of retainer spring 280 mechanically engages a portion of latch retainer 270.

In use, and with reference to FIGS. 6, 9 and 10, a distal lip 257 of plate 250 contacts a blocking surface 220 of lever 210 (FIG. 5), thus preventing rotation (i.e., in the substantial direction of arrow “C” in FIG. 6 of lever 210 until plate 250 is proximally moved a sufficient distance such that distal lip 257 proximally passes blocking surface 220 of lever 210. It is envisioned that rotation of approximation knob 22 such that anvil assembly 30 and shell assembly. 31 are approximated causes screw stop 40 to proximally translate a sufficient distance so tab portion 42 causes distal lip 257 to proximally pass blocking surface 220 (against the bias of plate spring 260). That is, once anvil assembly 30 and shell assembly 31 are approximated (e.g., clamping tissue therebetween), lever 210 is free to rotate (e.g., manually) from its first blocking position (FIGS. 4-6) to its second enabling position (FIGS. 7-9) in the substantial direction of arrow “C” (against the bias of safety spring 230), thus enabling actuation of firing trigger 20.

With regard to FIG. 9A, an enlarged view of the interaction between latch 212 and latch retainer 270 is shown. When lever 210 is rotated from its first blocking position to its second enabling position, latch 212 engages latch retainer 270. More particularly, angled surface 216 of latch 212 is configured to make initial contact with latch retainer 270. The force exerted by rotation of lever 210 causes angled surface 216 of latch 212 to distally translate latch retainer 270, with respect to plate 250, against the bias of retainer spring 280. After latch retainer 270 is distally translated and tooth 214 of latch 212 passes a securing member 272 of latch retainer 270, latch retainer 270 is translated proximally via the bias of retainer spring 280, such that securing member 272 is urged into the distance “d” between tooth 214 and surface 216 of lever 210. In this position, latch 212 is releasably retained by latch retainer 270, and actuation of firing trigger 20 is enabled.

If anvil assembly 30 and shell assembly 31 are moved towards their spaced position (e.g., via rotation of approximation knob 22 in the second direction), thus possibly unclamping tissue, safety mechanism 200 is configured such that lever 210 moves to its first, blocking position, thus preventing the firing of staples. In particular, as anvil assembly 30 and shell assembly 31 are moved towards their spaced position, screw stop 40 is moved distally. Thus, the portion 42 of screw stop 40 that had been in contact with and proximally urging distal portion 252 of plate 250, also moves distally. Consequently, the distal bias of plate spring 260 is not sufficiently resisted and plate 250 is distally translated. Upon distal translation of plate 250, latch retainer 270 and retainer spring 280 also translate distally (to a release point, as discussed below) such that latch retainer 270 releases latch 212. The release of latch 212, in combination with the bias asserted by safety spring 230, causes lever 210 to move towards its first, blocking position. Therefore, safety mechanism 200 prevents actuation of firing trigger 30 after unclamping of tissue (i.e., anvil assembly 30 and shell assembly 31 are moved towards their spaced (=approximated) position.

As can be appreciated, the tolerances of various components of safety mechanism 200 help determine the amount of unclamping that is sufficient to return lever 210 to its first, blocking position. For example, the release point may be dependent on an overlap “0” (FIG. 9A) between latch 212 and securing member 272 of latch retainer 270. It is envisioned that the overlap “0” may be between about 0.010 inches and about 0.080 inches, for example, depending on the desired effect. Other distances are also contemplated. In such an example, the smaller the overlap “0,” the lower amount of unclamping that will be necessary to cause lever 210 to return to its first, blocking position, and vice versa.

The present disclosure also contemplates the use of an indicator mechanism 100, as shown in FIGS. 4-9. In the first position, indicator 102 provides indication to a surgeon that the instrument is in an open, non-approximated position. In the second position, indicator 102 provides indication to a surgeon that the instrument has been approximated and is now in a fire-ready position. In the third position, indicator 102 provides indication to a surgeon that the instrument has been fired. Further details of indicator mechanism are shown and described in U.S. Pat. No. 7,303,106, incorporated hereinabove by reference.

The present disclosure also relates to a method of performing a surgical procedure. The method comprises the step of providing a surgical instrument, as described above, positioning the surgical instrument adjacent a surgical site, and moving anvil assembly 30 with respect to shell assembly 31 from its approximated position towards its spaced position to move the portion (e.g., lever 210) of safety mechanism 200 from its second position to its first position.

Further details of other features of surgical instrument 10, such as the approximation assembly, firing assembly, and lock out mechanism are disclosed in commonly-owned U.S. Pat. Nos. 7,168,604 and 7,303,106, the entire contents of each of which are incorporated by reference herein.

It will be understood that various modifications may be made to the embodiments disclosed herein. For example, the disclosed safety mechanism may be used with other types of surgical instruments for joining tissue, such as, for example, surgical stapling instrument with linear jaw members, surgical instruments with curved jaw members and vessel sealing instruments. Further details of a linear surgical stapling instrument are described in detail in commonly-owned U.S. Pat. No. 6,953,139 to Milliman et al., the entire contents of which are hereby incorporated by reference herein. An example of a commonly-owned vessel sealing instrument is disclosed in U.S. Pat. No. 7,118,570, the entire contents of which are hereby incorporated by reference herein. Therefore, the above description should not be construed as limiting, but merely as exemplifications of disclosed embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto. 

What is claimed is:
 1. A surgical instrument comprising: a handle assembly including a firing mechanism; an elongated body portion extending distally from the handle assembly; a head portion disposed adjacent a distal end of the elongated body portion, the head portion including an anvil assembly and a shell assembly that are moveable between spaced and approximated positions relative to one another, the shell assembly supporting a plurality of staples, the firing mechanism being actuatable to eject the plurality of staples from the shell assembly; and a safety mechanism disposed in mechanical cooperation with the handle assembly, the safety mechanism including a lever moveable from a first position preventing actuation of the firing mechanism to a second position permitting actuation of the firing mechanism, the lever being biased towards the first position, the safety mechanism including a latch retainer for releasably retaining the lever in the second position, wherein the latch retainer releases the lever from the second position in response to movement of the anvil and shell assemblies from the approximated position towards the spaced position relative to one another.
 2. The surgical instrument of claim 1, wherein the lever includes a latch configured to be releasably retained by the latch retainer to retain the lever in the second position.
 3. The surgical instrument of claim 1, wherein the safety mechanism includes a plate slidably disposed within the handle assembly, the plate defining an opening which receives a portion of the latch retainer therein.
 4. The surgical instrument of claim 3, wherein the latch retainer is biased proximally relative to the plate.
 5. The surgical instrument of claim 4, wherein the lever includes a latch disposed thereon, the latch retainer configured to engage the latch to retain the lever in the second position.
 6. The surgical instrument of claim 5, wherein the latch moves the latch retainer distally as the lever is moved from the first position to the second position.
 7. The surgical instrument of claim 3, wherein the plate is biased distally relative to the handle assembly.
 8. The surgical instrument of claim 7, further comprising an approximation mechanism for moving the anvil and shell assemblies between the spaced and approximated positions relative to one another, the approximation mechanism being engagable with the plate to move the plate proximally as the anvil and shell assemblies move relative to one another towards the approximated position.
 9. The surgical instrument of claim 1, wherein the handle assembly includes a firing trigger, the lever being pivotal from the first position in engagement with the firing trigger to the second position out of engagement with the firing trigger.
 10. A surgical instrument comprising: a handle assembly including a firing mechanism; an elongated body portion extending distally from the handle assembly; a head portion disposed adjacent a distal end of the elongated body portion, the head portion including an anvil assembly and a shell assembly, the head portion having a spaced position in which the anvil assembly is spaced from the shell assembly and an approximated position in which the anvil assembly is approximated to the shell assembly, the shell assembly supporting a plurality of staples, the firing mechanism being actuatable to eject the plurality of staples from the shell assembly; and a safety mechanism disposed in mechanical cooperation with the handle assembly, the safety mechanism including a lever moveable from a first position preventing actuation of the firing mechanism to a second position permitting actuation of the firing mechanism, the lever being biased towards the first position, the safety mechanism including a latch retainer for releasably retaining the lever in the second position, wherein the latch retainer releases the lever from the second position in response to movement of the head portion towards the spaced position.
 11. The surgical instrument of claim 10, wherein the lever includes a latch configured to be releasably retained by the latch retainer to retain the lever in the second position.
 12. The surgical instrument of claim 10, wherein the safety mechanism includes a plate slidably disposed within the handle assembly, the plate defining an opening which receives a portion of the latch retainer therein.
 13. The surgical instrument of claim 12, wherein the latch retainer is biased proximally relative to the plate.
 14. The surgical instrument of claim 13, wherein the lever includes a latch disposed thereon, the latch retainer configured to engage the latch to retain the lever in the second position.
 15. The surgical instrument of claim 14, wherein the latch moves the latch retainer distally as the lever is moved from the first position to the second position.
 16. The surgical instrument of claim 12, wherein the plate is biased distally relative to the handle assembly.
 17. The surgical instrument of claim 16, further comprising an approximation mechanism for transitioning the head portion between the spaced and approximated positions, the approximation mechanism being engagable with the plate to move the plate proximally as the head portion moves towards the approximated position.
 18. The surgical instrument of claim 10, wherein the handle assembly includes a firing trigger, the lever being pivotal from the first position in engagement with the firing trigger to the second position out of engagement with the firing trigger. 